This invention pertains to tubular type heat exchangers for use in heat recovery steam generators (HRSG), and particularly pertains to such heat exchangers units utilizing inverted U-shaped tubes connected to elongated parallel headers for economizers and superheaters used in such generators.
Tubular type heat exchangers such as used in economizers or superheaters in heat recovery steam generators usually utilize pairs of upper and lower headers which are connected together by multiple vertically-oriented tubes, so that hot gases such as derived from a gas turbine exhaust can flow transversely across the tubes to heat a fluid flowing vertically in the tubes, so as to generate pressurized steam therein. Such heat exchangers having various tube configurations are known, for example, as disclosed by U.S. Pat. Nos. 4,644,067 to Haneda et al; 4,685,426 to Kidaloski et al; and 4,944,252 to Motai et al. However, such heat exchanger designs utilizing pairs of upper and lower headers are thermodynamically less efficient and are undesirably expensive, so that improved configurations and designs for such heat exchangers have been sought.